[Scipy-tickets] [SciPy] #1298: Orthogonal polynomials return infinity when evaluated at -1

SciPy Trac scipy-tickets@scipy....
Tue Oct 12 09:30:46 CDT 2010


#1298: Orthogonal polynomials return infinity when evaluated at -1
---------------------------+------------------------------------------------
 Reporter:  joelphillips   |       Owner:  pv   
     Type:  defect         |      Status:  new  
 Priority:  high           |   Milestone:  0.9.0
Component:  scipy.special  |     Version:  0.8.0
 Keywords:                 |  
---------------------------+------------------------------------------------

Comment(by joelphillips):

 The error is in scipy/special/cephes/hyp2f1.c

 140     if (d <= 0 && x == 1)
 141         goto hypdiv;

 The most benign fix I can see would be:

 140     if (d <= 0 && x == 1 && !(neg_int_a || neg_int_b))
 141         goto hypdiv;

 which would only raise the error if the function is non-polynomial
 (although I'm not sure what happens if c is a negative non-integer).
 However, that could be too restrictive.  This really needs attention by
 someone who's spent more time with hypergeometric functions than I have.

-- 
Ticket URL: <http://projects.scipy.org/scipy/ticket/1298#comment:1>
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